SELECTED CASEAn asymptomatic 34-year-old white man was referred to the Lipid Clinic of the National Heart, Lung, and Blood Institute for atherosclerotic cardiovascular disease risk assessment. His father died at the age of 39 years of a myocardial infarction, and his 2 paternal uncles developed symptomatic coronary artery disease by the age of 40 years. The search for conventional cardiovascular disease risk factors was unrevealing. The patient exercised regularly and had never smoked tobacco products. Physical examination revealed a normotensive man within 5% of his ideal body weight. His fasting concentrations of blood glucose (5.33 mmol/L [96 mg/dL]), low-density lipoprotein cholesterol (LDL-C) (1.76 mmol/L [68 mg/ dL]) and high-density lipoprotein cholesterol (HDL-C) (1.06 mmol/L [41 mg/dL]) were all within normal limits. However, his fasting plasma triglyceride concentration was increased (6.64 mmol/L [588 mg/dL]) as was his apolipoprotein B concentration at 3.90 mmol/L (151 mg/dL) (normal range, 1.94-3.33 mmol/L [75-129